Pharmacokinetics of topically applied ophthalmic drugs.

Pharmacokinetic applications in recent years have led to significant advances in systemic drug therapy, but applications to topical, ophthalmic therapy have been far less numerous. Pharmacokinetics is the study of the time course of the absorption, distribution, metabolism, and elimination of an administered drug. Thus, it includes the quantitation of such elements of drug bioavailability as tear dilution, drug binding, and vehicle effects; factors affecting corneal absorption and subsequent tissue distribution; dosage form effects; and pathways of elimination. These factors are important because they significantly influence the clinical responses to administered drugs, in some instances to a profound degree. These elements and their clinical implications are discussed along with some recent applications, exemplified with data from studies on frequently prescribed drugs.